Digital imaging device with enhanced dynamic range and operating method thereof

ABSTRACT

A digital imaging device including a sensor array, an analog front end and a digital back end. The sensor array is configured to output black pixel data and normal pixel data. The analog front end is configured to amplify the black pixel data and the normal pixel data with a gain, and calibrate the amplified black pixel data and the amplified normal pixel data with a calibration value. The digital back end is configured to digitize the amplified and calibrated black pixel data, calculate a data offset according to digital black pixel data, determine a dynamic adjust scale, calculate the calibration value according to the gain, the data offset and the dynamic adjust scale, and adjust the gain according to the dynamic adjust scale.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan PatentApplication Serial Number 104109453, filed on Mar. 24, 2015, the fulldisclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to an imaging device, moreparticularly, to a digital imaging device with an enhanced dynamic rangeand an operating method thereof.

2. Description of the Related Art

An image sensor usually includes a sensor array which senses lightenergy and outputs an analog signal, e.g., a current signal, a voltagesignal or charges. The analog signal is then processed by an analogpreprocessing and a digital post-processing to be configured as framedata.

When a photoelectric element, e.g., photodiode, outputs a photocurrentnot under an absolute zero temperature, the photocurrent usuallyaccompanies with dark current, which affects a real signal of the lightenergy sensed by the photoelectric element. Therefore, conventionally aso-called black level calibration (BLC) is used to eliminate the darkcurrent signal. The black level calibration is generally implemented bydisposing the black pixel in the sensor array to generate dark currentto be used as a calibration value. As the name implies, the dark pixelis shielded from receiving external light, and generally the black pixelis formed by covering a shielding layer over a normal pixel.

Referring to FIG. 1, it is a schematic diagram of a conventional imagesensor 9, which includes a sensor array 91, a correlated double samplingcircuit (CDS) 93, an amplifier 95, an analog to digital converter (ADC)97, a black level average circuit 98 and a subtractor 99.

The sensor array 91 includes a plurality of black pixels 91 b and aplurality of normal pixels 91 n. The correlated double sampling circuit93 temporarily stores analog pixel data sequentially outputted by pixelsin each row of the sensor array 91. The amplifier 95 amplifies theanalog pixel data and transmits the amplified data to the analog todigital converter 97 (for example, 11 bits ADC) for digitization, asshown in FIG. 2, wherein digital pixel data of the normal pixels 91 n iswithin a digital range of 1024-2047, and the digital pixel data of theblack pixels 91 b is near the digital value of 1023. The black levelaverage circuit 98 calculates an average value of the digital pixel dataof the black pixels 91 b as a black level calibration value (BLC). Thesubtractor 99 subtracts the black level calibration value BLC from thedigital pixel data of the normal pixels 91 n to allow the digital pixeldata of the normal pixel 91 n to be within a valid dynamic range of0-1023.

However, as shown in FIG. 3, the analog pixel data outputted by thenormal pixels 91 n can be affected by the pixel itself, the correlateddouble sampling circuit 93 and the amplifier 95 to have an offset. Theoffset leads the analog pixel data inputted into the analog to digitalconverter 97 to be out of the dynamic range (as circled by dash lines)of the analog to digital converter 97, and lowers the valid dynamicrange after the black level calibration.

SUMMARY

Accordingly, the present disclosure provides a digital imaging devicewith an optimized dynamic range and an operating method thereof.

The present disclosure provides a digital imaging device and anoperating method thereof that adjust analog pixel data in an analogstage to correspond to a dynamic range of an analog to digital converterso as to effectively utilize the dynamic range of the analog to digitalconverter thereby increasing the signal resolution and improving thesignal quality.

The present disclosure provides a digital imaging device including asensor array, a sample hold circuit, an amplifier, a subtractor, ananalog to digital converter and a digital back end. The sensor arrayincludes a plurality of black pixels and a plurality of normal pixels,wherein the black pixels output black pixel data and the normal pixelsoutput normal pixel data. The sample hold circuit temporarily holds theblack pixel data and the normal pixel data. The amplifier amplifies theblack pixel data and the normal pixel data with a gain. The subtractorsubtracts a calibration value from the amplified black pixel data andthe amplified normal pixel data. The analog to digital converterreceives amplified and calibrated pixel data to output digital blackpixel data and digital normal pixel data. The digital back endcalculates a data offset according to the digital black pixel data,determines a dynamic adjustment scale, calculates the calibration valueaccording to the gain, the data offset and the dynamic adjustment scale,and adjusts the gain according to the dynamic adjustment scale

The present disclosure further provides an operating method of a digitalimaging device. The digital imaging device includes a sensor array, ananalog front end and a digital back end, wherein the sensor arrayoutputs black pixel data and normal pixel data, the analog front endamplifies and calibrates the black pixel data and the normal pixel data,and the digital back end processes digital pixel data. The operatingmethod includes: amplifying the black pixel data and the normal pixeldata with a gain, calibrating data ranges of the amplified black pixeldata and the amplified normal pixel data with a calibration value,digitizing the amplified and calibrated black pixel data and digitizingthe amplified and calibrated normal pixel data, calculating a dataoffset according to digital black pixel data, determining a dynamicadjustment scale, calculating the calibration value according to thegain, the data offset and the dynamic adjustment scale, and adjustingthe gain according to the dynamic adjustment scale.

The present disclosure further provides a digital imaging deviceincluding a sensor array, an analog front end and a digital back end.The sensor array includes a plurality of black pixels and a plurality ofnormal pixels, wherein the black pixels output black pixel data and thenormal pixels output normal pixel data. The analog front end amplifiesthe black pixel data and the normal pixel data with a gain, andcalibrates data ranges of the amplified black pixel data and theamplified normal pixel data with a calibration value. The digital backend digitizes the amplified and calibrated black pixel data, calculatesa data offset according to digital black pixel data, determines adynamic adjustment scale, calculates a maximum calibration value and aminimum calibration value according to the gain, the data offset and thedynamic adjustment scale, calculate an average value of the maximumcalibration value and the minimum calibration value to be configured asthe calibration value, and adjusts the gain according to the dynamicadjustment scale.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a conventional image sensor.

FIG. 2 is a schematic diagram of a black level calibration of the imagesensor in FIG. 1.

FIG. 3 is another schematic diagram of a black level calibration of theimage sensor in FIG. 1.

FIG. 4 is a schematic diagram of a digital image sensor according to oneembodiment of the present disclosure.

FIG. 5 is a schematic diagram of an operation of a digital image sensoraccording to one embodiment of the present disclosure.

FIG. 6 is a flow chart of an operating method of a digital imagingdevice according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Please refer to FIG. 4, it is a schematic diagram of a digital imagingdevice according to one embodiment of the present disclosure. Thedigital imaging device 100 includes a sensor array 11, an analog frontend and a digital back end 18, wherein the analog front end is coupledto output terminals of the sensor array 11 (e.g. a plurality of outputelectrodes), and the digital back end 18 is coupled to the analog frontend.

The sensor array 100 includes a plurality of black pixels 11 b and aplurality of normal pixels 11 n, wherein the black pixels 11 b outputblack pixel data Sb and the normal pixels 11 n output normal pixel dataSn. The analog front end amplifies and calibrates the black pixel dataSb and the normal pixel data Sn to allow a data range of the normalpixel data Sn to match a dynamic range (described later) of thedigitization as much as possible. The digital back end 18 processesdigital pixel data.

The sensor array 100 includes a plurality of pixels arranged in an array(e.g. 8×8 pixel array shown in FIG. 4), wherein a plurality of blackpixels 11 b are shown the region filled by oblique lines and a pluralityof normal pixels 11 n are shown as the non-filled region. It should bemention that the arrangement of the black pixels 11 b is not limited tothat shown in FIG. 4. Pixel structures of the black pixels 11 b and thenormal pixels 11 n are the same, e.g., both of the black pixels 11 b andthe normal pixels 11 n including a photodiode and a plurality oftransistors. The difference between the black pixels 11 b and the normalpixels 11 n is that a shielding layer (e.g. a metallic layer ornon-metallic layer) is further formed over the black pixels 11 b toblock the black pixels 11 b from receiving the light from outside,wherein the method of forming a shielding layer on the normal pixel isknown and not an object of the present disclosure, and thus detailsthereof are not described herein. Accordingly, black pixel data Sboutputted by the black pixels 11 b only relates to the dark current,wherein the dark current relates to, e.g., the surrounding temperature.Normal pixel data Sn outputted by the normal pixels 11 n relates to boththe dark current and photocurrent which is induced by external lightirradiating the pixels, wherein the photocurrent, e.g., is positivelycorrelated with the intensity of ambient light. The black pixel data Sbin the present disclosure is used to obtain a data offset caused bypixels themselves and the analog front end (describing later).

Pixel data of the sensor array 100 is scanned and read by a row scancontroller 12 r and a column read controller 12 c, and the timing ofscanning and reading of the pixel data is controlled by a timingcontroller, wherein a method of a timing controller controlling a rowscan controller and a column read controller to scan and read pixel datais known and not an object of the present disclosure, and thus detailsthereof are not described herein.

In the present disclosure, the analog front end amplifies the blackpixel data Sb and the normal pixel data Sn with a gain G, and calibratesdata ranges of the amplified black pixel data Sba and the amplifiednormal pixel data Sna with a calibration value DAC to match a dynamicrange of the digitization as much as possible, wherein the calibrationvalue DAC and the gain G are controlled or provided by the digital backend 18.

In some embodiments, the analog front end includes a sample hold circuit13, an amplifier 15, a gain controller 151 and a subtractor 16. Itshould be mentioned that although FIG. 4 shows that an analog to digitalconverter (ADC) 17 is included in the analog front end, the presentdisclosure is not limited thereto. In other embodiments, the analog todigital converter 17 is included in the digital back end 18 withoutparticular limitations as long as the analog to digital converter 17 isable to receive amplified and calibrated pixel data and output digitalblack pixel data Db and digital normal pixel data Dn. In other words,the shown position of the analog to digital converter 17 is onlyintended to describe, and it is possible that the analog to digitalconverter 17 is included in an analog front end, in a digital back endor outside of the analog front end and the digital back end. Besides,the analog front end further includes other elements, e.g., a filtercircuit, and since they are not directly related to the presentdisclosure, and thus derails thereof are not described herein.

The sample hold circuit 13 is, for example, a correlated double samplingcircuit (CDS) which temporarily holds the black pixel data Sb and thenormal pixel data Sn samples from the sensor array 11, and an operationof the sample hold circuit 13 is controlled by the timing controller 14.For example, the sample hold circuit 13 temporarily saves pixel data ofone row of black pixels 11 b or one row of normal pixels 11 n every timeto sequentially sample and hold the pixel data of all pixels of thesensor array 11 within a frame period.

The amplifier 15 is, for example, an integrated programmable gainamplifier (IPGA) and connects to the sample hold circuit 13 to receivethe pixel data held in the sample hold circuit 13. The amplifier 15 iscontrolled by the gain controller 151 to amplify the black pixel data Sband the normal pixel data Sn with a gain G (or an adjusted gain NG) togenerate amplified black pixel data Sba and amplified normal pixel dataSna. In the present disclosure, the amplifier 15 includes a single stageamplification unit or cascaded multistage amplification units withoutparticular limitations.

The subtractor 16 subtracts a calibration value DAC from the amplifiedblack pixel data Sba and the amplified normal pixel data Sna to allow apixel data range to match a dynamic range of the analog to digitalconverter 17. According to the calibration value DAC provided by thedigital back end 18, the subtractor 16 is implemented by an adder. Inaddition, when the amplifier 15 includes a single stage amplificationunit, the subtractor 16 (or an adder) is coupled to an output terminalof the single stage amplification unit. When the amplifier 15 includesmultistage amplification units, the subtractor 16 (or an adder) iscoupled between the amplification units or coupled to an output terminalof a final stage amplification unit among the amplification unitswithout particular limitations. Furthermore, when the amplifier 15includes multistage amplification units, the analog front end includesseveral subtractors or adders to calculate a difference between aplurality of calibration values DAC respectively with the amplifiedblack pixel data Sba and the amplified normal pixel data Sna.

The digital back end 18 digitizes amplified and calibrated black pixeldata and digitizes amplified and calibrated normal pixel data,calculates a data offset Δ according to digital black pixel data Db,determines a dynamic adjustment scale M, calculates the calibrationvalue DAC according to the gain G, the data offset Δ and the dynamicadjustment scale M, and adjusts the gain G according to the dynamicadjustment scale M. An embodiment of the operation of the digital backend 18 is described below. As mentioned above, when the analog todigital converter 17 is in the analog front end, the step of digitizingamplified and calibrated black pixel data and digitizing amplified andcalibrated normal pixel data is processed in the analog front end.

Referring to FIGS. 4 and 5, FIG. 5 is a schematic diagram of theoperation of a digital image sensor according to one embodiment of thepresent disclosure, wherein the operation of optimizing the data rangeis described by an initial step, an adjustment step and a calibrationstep. In addition, FIG. 5 is described by an 11 bits dynamic range, butnot limited thereto. A number of sampling bits of the analog to digitalconverter 17 is determined according to the device actually being used.

In the initial step, a data range of digital normal pixel data Dn (e.g.Vref=1 mV) which is converted by the analog to digital converter 17 issubstantially positive values, and a data range of digital black pixeldata Db (e.g. Vref=1 mV) is substantially around, but not limited to, adigital value of 1023, wherein digital values outputted by the analog todigital converter 17 are all positive values (shown as digital values of0 to 2047 in figure). Digital values of 1024 to 2047 are defined aspositive values and digital values of 0 to 1023 are defined as negativevalues herein.

Referring to FIG. 5, in the initial step, a data range of the digitalnormal pixel data Dn is substantially a half of a sample dynamic rangeof the analog to digital converter 17. The present disclosure is toallow the data range of the amplified and calibrated normal pixel datato match the digitization range (e.g. digital values of 0 to 2047) ofthe analog to digital converter 17 as much as possible.

For example, in a first frame, the digital back end 18 controls, throughthe gain controller 151, the amplifier 15 to amplify the normal pixeldata Sn and the black pixel data Sb with a gain G To increase a validdynamic range, the digital back end 18 calculates a dynamic adjustmentscale M and a calibration value DAC with the adjustment step and thecalibration step to calibrate the amplified normal pixel data Snaaccording to the calibration value DAC in a second frame (e.g. a frameafter the first frame), wherein a gain in the second frame is alsoadjusted according to the dynamic adjustment scale M to increase thevalid dynamic range. Because the gain controller 151 is controlled bythe digital back end 18, the digital back end 18 has already known avalue of the gain G.

The digital back end 18 calculates a difference value between an averagevalue of the digital black pixel data Db and a reference value (e.g. adigital value of 1023, but not limited to) and divides the differencevalue by the gain G to be used as the data offset Δ, wherein the dataoffset Δ is caused by, e.g., pixels and the sample hold circuit 13, andthe data offset Δ is the reason causing the shrinkage of the validdynamic range, as shown in FIG. 3. The reference value is selected as anideal value which is outputted by the black pixels 11 b, i.e. a valuenot having the data offset Δ. The data offset Δ is amplified to GΔ bythe amplifier 15, e.g., +G Δ and −G Δ shown in the adjustment step.

The digital back end 18 amplifies digital normal pixel data Dn with thedynamic adjustment scale M to generate MDn. If the data offset Δ doesnot exist, when the dynamic adjustment scale M is selected as 2, thedynamic range of the analog to digital converter 17 is completelyusable. However, as there is the data offset Δ, the dynamic adjustmentscale M is selected, e.g., between 1.5-1.9 depending on the data offsetΔ obtained by the digital back end 18. For example, affected by the dataoffset Δ, the digital normal pixel data MDn after being adjusted shiftsupwardly or downwardly by GΔ, e.g., MDn+GΔ and MDn−GΔ shown in theadjustment step.

In one embodiment, the digital back end 18 determines the dynamicadjustment scale M according to a look-up table. For example, inside oroutside the digital back end 18 there is a storage element 19, e.g., adynamic random access memory (RAM) or read only memory (ROM) for storinga look-up table (LUT). The look-up table pre-stores the relationshipbetween a plurality of data offsets Δ and a plurality of gains G withrespect to a plurality of the dynamic adjustment scales M. Accordingly,the digital back end 18 determines the dynamic adjustment scale M bycomparing a current gain and a current data offset (e.g. obtainedaccording to the first frame) with the look-up table.

In another embodiment, to optimize the dynamic adjustment scale M, thedigital back end 18 is further able to determine the dynamic adjustmentscale M according to an interaction algorithm. For example, the digitalback end 18 calculates a maximum calibration value DACmax and a minimumcalibration value DACmin according to the gain G, the data offset Δ andthe dynamic adjustment scale M. When the maximum calibration valueDACmax is larger than the minimum calibration value DACmin, the dynamicadjustment scale M is increased, a new maximum calibration value and anew minimum calibration value are recalculated, and the new maximumcalibration value and the new minimum calibration value are compared.The dynamic adjustment scale M is continuously increased in this manneruntil the new maximum calibration value is smaller than or equal to thenew minimum calibration value. An associated maximum dynamic adjustmentM when the new maximum calibration value is still larger than the newminimum calibration value is selected as an optimum dynamic adjustmentscale.

In one embodiment, the digitalization of the analog to digital converter17 is assumed to have a dynamic range (e.g. digital values of 11 bitsshown in FIG. 5, 0 to 2047). The maximum calibration value DACmax isobtained by subtracting a product of the gain G and the data offset Δfrom a half of the dynamic range, i.e. DACmax=1024−(G×Δ), wherein themaximum calibration value DACmax is to prevent the shifted normal pixeldata MDn−GΔ from exceeding a minimum value of the dynamic range (asshown in the calibration step). The minimum calibration value DACmin isobtained by subtracting a half of the dynamic range from a summation ofa product of the half of the dynamic range and the dynamic adjustmentscale M and a product of the gain G and the data offset Δ, i.e.DACmin=(1024×M)+(G×Δ)−1024, wherein the minimum calibration value DACminis to prevent the offset normal pixel data MDn+GΔ from exceeding amaximum value of the dynamic range (as shown in the calibration step).

After the digital back end 18 calculates a maximum calibration valueDACmax and a minimum calibration value DACmin according to the gain G,the data offset Δ, and the dynamic adjustment scale M (as shown in thecalibration step), the digital back end 18 further calculates an averagevalue of the maximum calibration value DACmax and the minimumcalibration value DACmin to be used as the calibration value DAC. Byusing the average value as the calibration value DAC, the amplified andcalibrated normal pixel data does not exceed the dynamic range of theanalog to digital converter 17.

Then, after the digital back end 18 converts the calibration value DACto an analog direct current value (e.g. by a digital to analogconverter), the analog direct current value is provided to a subtractor16 of the analog front end. Meanwhile, the digital back end 18multiplies an unadjusted gain G by a multiple N to adjust the gain toNG, and the multiple N is a quotient of the dynamic adjustment scale Mdivided by the gain G. Accordingly, because the multiple N and thedynamic adjustment scale M is obtained by current data offset Δ andcurrent gain G, MDn is larger than Dn and within the dynamic range so asto increase the valid dynamic range and the image quality.

It should be mention that the three steps of FIG. 5 are all obtained inthe digital back end 18, e.g., calculated by a digital signal processor(DSP) therein according to the digital black pixel data Db and thedigital normal pixel data Dn using an algorithm implemented by software,hardware and/or firmware.

Referring to FIG. 6, it is a flow chart of an operating method of adigital imaging device according to one embodiment of the presentdisclosure, including following steps: amplifying black pixel data andnormal pixel data with a gain (step S61); calibrating data ranges of theamplified black pixel data and the amplified normal pixel data with acalibration value (step S62); digitizing the amplified and calibratedblack pixel data and digitizing the amplified and calibrated normalpixel data (step S63); calculating a data offset according to digitalblack pixel data (step S64); determining a dynamic adjustment scale(step S65); calculating the calibration value according to the gain, thedata offset and the dynamic adjustment scale (step S66); and adjustingthe gain according to the dynamic adjustment scale (step S67).

Please also refer to FIGS. 4 and 5, details of the operating method aredescribed hereinafter.

Step S61: For example, in a first frame (e.g. an image frame capturedwhen the digital imaging device 100 starts operating or leaves a sleepmode), the sensor array 11 outputs a plurality of black pixel data Sband a plurality of normal pixel data Sn. The digital back end 18controls the amplifier 15 by the gain controller 151 to amplify theblack pixel data Sb and the normal pixel data Sn with a gain G togenerate amplified black pixel data Sba and amplified normal pixel dataSna.

Step S62: The digital back end 18 outputs a calibration value DAC to thesubtractor 16 to calibrate data ranges of the amplified black pixel dataSba and the amplified normal pixel data Sna, wherein the calibrationvalue DAC is, for example an analog direct current value. In addition,corresponding to the first frame, an initial value of the calibrationvalue DAC is, for example 0, but not limited thereto. Corresponding tothe data frame after the first frame, the calibration value DAC isdetermined according to the calculation result of the digital back end18.

Step S63: The analog to digital converter 17 digitizes the amplified andcalibrated black pixel data and the amplified and calibrated normalpixel data to respectively generate digital black pixel data Db anddigital normal pixel data Dn, wherein the amplification is performed bythe amplifier 15, whereas the calibration is performed by the subtractor16.

Step S64: The digital back end 18 calculates a data offset Δ accordingto the digital black pixel data Db. As mentioned above, the digital backend 18, for example, calculates a difference value between an averagevalue of the digital black pixel data Db and a reference value (e.g.,shown as 1023 in FIG. 5, but not limited to) to be used as the dataoffset ΔG which represents data offset caused by other reasons insteadof photocurrent.

Step S65: The digital back end 18 also determines a dynamic adjustmentscale M, as shown in FIG. 5. In one embodiment, the digital back end 18compares a current gain G and a current data offset Δ (e.g. obtainedaccording to the first frame) with a look-up table to determine thedynamic adjustment scale M, wherein the look-up table pre-stores arelationship of a plurality of data offsets and a plurality of gainswith respect to a plurality of dynamic adjustment scales, and thelook-up table is stored in the storage element 19. In anotherembodiment, the digital back end 18 determines the dynamic adjustmentscale M according to an iteration algorithm. For example, the digitalback end 18 calculates a maximum calibration value DACmax and a minimumcalibration value DACmin according to a current gain, a current dataoffset and a current dynamic adjustment scale (as shown in FIG. 5). Whenthe maximum calibration value DACmax is larger than the minimumcalibration value DACmin, the dynamic adjustment scale M is increased, anew maximum calibration value and a new minimum calibration value arerecalculated, and the dynamic adjustment scale M is continuouslyincreased until the new maximum calibration value is smaller than orequal to the new minimum calibration value, wherein the current dynamicadjustment scale is determined, for example, according to the currentgain and the current data offset (e.g. determined according to thelook-up table). When the new maximum calibration value is smaller thanor equal to the new minimum calibration value, a maximum dynamicadjustment scale that allows the new maximum calibration value still tobe larger than the new minimum calibration value is selected as anoptimum dynamic adjustment scale.

Step S66: The digital back end 18 calculates the calibration value DACaccording to the gain G, the data offset Δ and the dynamic adjustmentscale M. As mentioned above, the digital back end 18 calculates amaximum calibration value DACmax and a minimum calibration value DACmin(as shown in FIG. 5) according to the gain G, the data offset Δ and thedynamic adjustment scale M (or the optimum dynamic adjustment scale),and calculates an average value of the maximum calibration value DACmaxand the minimum calibration value DACmin as the calibration value DAC toprevent the amplified and calibrated normal pixel data from exceedingthe dynamic range of the analog to digital converter 17.

Step S67: Finally, the digital back end 18 transmits the dynamicadjustment scale M to the subtractor 16 and adjusts the gain G accordingto the dynamic adjustment scale M. For example, the digital back end 18controls the gain controller 151 to multiply the gain G by a multiple Nto generate a new gain NG, wherein the multiple N is a quotient of thedynamic adjustment scale M divided by the gain G.

Next, the sensor array 11 outputs a second frame, and the analog frontend processes the black pixel data Sb and the normal pixel data Sn withthe dynamic adjustment scale M and the new gain NG to effectivelyutilize the dynamic range of the analog to digital converter 17.

The digital imaging device 100 is able to perform the operating methodof FIG. 6 every predetermined time and/or each time of the startingprocedure or leaving the sleep mode without performing corresponding toevery image frame.

It should be mention that, a sequence of the steps S64-S66 performed bythe digital back end 18 is not limited to that shown in FIG. 6 dependingon the circuit design or the algorithm in the digital back end 18. Thesteps are able to be calculated simultaneously or sequentially withoutparticular limitations.

As mentioned above, the conventional imaging device is affected by thesignal offset to have a smaller valid dynamic range. Therefore, thepresent disclosure provides a digital imaging device (FIG. 4) and anoperating method thereof that optimize the data range in the analogstage to match a dynamic range of an analog to digital converter as muchas possible to further improve the signal resolution and the imagequality.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A digital imaging device comprising: a sensorarray comprising a plurality of black pixels and a plurality of normalpixels, wherein the black pixels are configured to output black pixeldata and the normal pixels are configured to output normal pixel data; asample hold circuit configured to temporarily hold the black pixel dataand the normal pixel data; an amplifier configured to amplify the blackpixel data and the normal pixel data with a gain; a subtractorconfigured to subtract a calibration value from the amplified blackpixel data and the amplified normal pixel data; an analog to digitalconverter configured to receive amplified and calibrated pixel data tooutput digital black pixel data and digital normal pixel data; and adigital back end configured to calculate a data offset according to thedigital black pixel data, determine a dynamic adjustment scale,calculate the calibration value according to the gain, the data offsetand the dynamic adjustment scale, and adjust the gain according to thedynamic adjustment scale.
 2. The digital imaging device as claimed inclaim 1, wherein the digital back end is configured to calculate amaximum calibration value and a minimum calibration value according tothe gain, the data offset and the dynamic adjustment scale, andcalculate an average value of the maximum calibration value and theminimum calibration value to be configured as the calibration value. 3.The digital imaging device as claimed in claim 1, wherein the digitalback end is configured to calculate a difference value between anaverage value of the digital black pixel data and a reference value tobe configured as the data offset.
 4. The digital imaging device asclaimed in claim 1, wherein the digital back end is configured tocompare the gain and the data offset with a look-up table to determinethe dynamic adjustment scale.
 5. The digital imaging device as claimedin claim 1, wherein the digital back end is configured to calculate amaximum calibration value and a minimum calibration value according tothe gain, the data offset and the dynamic adjustment scale, increase thedynamic adjustment scale and recalculate a new maximum calibration valueand a new minimum calibration value when the maximum calibration valueis larger than the minimum calibration value, and continuously increasethe dynamic adjustment scale until the new maximum calibration value issmaller than or equal to the new minimum calibration value.
 6. Thedigital imaging device as claimed in claim 1, wherein the amplifiercomprises a single stage amplification unit, and the subtractor iscoupled to an output terminal of the single stage amplification unit. 7.The digital imaging device as claimed in claim 1, wherein the amplifiercomprises multistage amplification units, and the subtractor is coupledbetween the amplification units or coupled to an output terminal of afinal stage amplification unit among the amplification units.
 8. Thedigital imaging device as claimed in claim 1, wherein the dynamicadjustment scale is between 1.5-1.9.
 9. An operating method of a digitalimaging device, the digital imaging device comprising a sensor array, ananalog front end and a digital back end, wherein the sensor array isconfigured to output black pixel data and normal pixel data, the analogfront end is configured to amplify and calibrate the black pixel dataand the normal pixel data, and the digital back end is configured toprocess digital pixel data, the operating method comprising: amplifyingthe black pixel data and the normal pixel data with a gain; calibratingdata ranges of the amplified black pixel data and the amplified normalpixel data with a calibration value; digitizing the amplified andcalibrated black pixel data and digitizing the amplified and calibratednormal pixel data; calculating a data offset according to digital blackpixel data; determining a dynamic adjustment scale; calculating thecalibration value according to the gain, the data offset and the dynamicadjustment scale; and adjusting the gain according to the dynamicadjustment scale.
 10. The operating method as claimed in claim 9,wherein the calculating the calibration value comprises: calculating amaximum calibration value and a minimum calibration value according tothe gain, the data offset and the dynamic adjustment scale; andcalculating an average value of the maximum calibration value and theminimum calibration value to be configured as the calibration value. 11.The operating method as claimed in claim 9, wherein the determiningcomprises: comparing the gain and the data offset with a look-up tableto determine the dynamic adjustment scale.
 12. The operating method asclaimed in claim 9, wherein the determining comprises: calculating amaximum calibration value and a minimum calibration value according tothe gain, the data offset and the dynamic adjustment scale; increasingthe dynamic adjustment scale and recalculating a new maximum calibrationvalue and a new minimum calibration value when the maximum calibrationvalue is larger than the minimum calibration value; and continuouslyincreasing the dynamic adjustment scale until the new maximumcalibration value is smaller than or equal to the new minimumcalibration value.
 13. The operating method as claimed in claim 9,wherein the adjusting comprises: multiplying the gain by a multiple,wherein the multiple is a quotient of the dynamic adjustment scaledivided by the gain.
 14. The operating method as claimed in claim 9,wherein the calculating the data offset comprises: calculating adifference value between an average value of the digital black pixeldata and a reference value to be configured as the data offset.
 15. Adigital imaging device comprising: a sensor array comprising a pluralityof black pixels and a plurality of normal pixels, wherein the blackpixels are configured to output black pixel data and the normal pixelsare configured to output normal pixel data; an analog front endconfigured to amplify the black pixel data and the normal pixel datawith a gain, and calibrate data ranges of the amplified black pixel dataand the amplified normal pixel data with a calibration value; and adigital back end configured to digitize the amplified and calibratedblack pixel data, calculate a data offset according to digital blackpixel data, determine a dynamic adjustment scale, calculate a maximumcalibration value and a minimum calibration value according to the gain,the data offset and the dynamic adjustment scale, calculate an averagevalue of the maximum calibration value and the minimum calibration valueto be configured as the calibration value, and adjust the gain accordingto the dynamic adjustment scale.
 16. The digital imaging device asclaimed in claim 15, wherein the amplified and calibrated black pixeldata is digitized based on a dynamic range, the maximum calibrationvalue is obtained by subtracting a product of the gain and the dataoffset from a half of the dynamic range, and the minimum calibrationvalue is obtained by subtracting the half of the dynamic range from asummation of a product of the half of the dynamic range and the dynamicadjustment scale and a product of the gain and the data offset.
 17. Thedigital imaging device as claimed in claim 15, wherein the digital backend is configured to determine the dynamic adjustment scale according toan iteration algorithm.
 18. The digital imaging device as claimed inclaim 15, wherein the digital back end is configured to determine thedynamic adjustment scale according to a look-up table, and the look-uptable is configured to pre-store a relationship of a plurality of dataoffset and a plurality of gains with respect to a plurality of dynamicadjustment scales.
 19. The digital imaging device as claimed in claim15, wherein the digital back end is configured to multiply the gain by amultiple to adjust the gain, and the multiple is a quotient of thedynamic adjustment scale divided by the gain.
 20. The digital imagingdevice as claimed in claim 15, wherein the digital back end isconfigured to calculate a difference value between an average value ofthe digital black pixel data and a reference value to be configured asthe data offset.